The hydrogenases isolated from Desulfovibrio gigas and Desulfovibrio baculatus, and the carbon monoxide dehydrogenases (CODH's) from Clostridium thermoaceticum and Rhodospirillum rubrum are Ni containing enzymes in which the Ni plays an important role in enzymatic activity. Understanding the oxidation state changes that Ni undergoes during the catalytic cycle in these enzymes is important in determining the mechanism of activity. We have developed a method of correlating the L-edge x-ray absorption spectral features with the Ni oxidation and spin state of Ni compounds, and have previously applied this method to the CODH from C. thermoaceticum . We propose to collect L-edge x-ray absorption data and to apply the same analysis method to the hydrogenases from D. gigas and D. baculatus in order to better understand the changes in electronic structure of the Ni during the catalytic cycles.